As I said before - it's spring evaluation time. Did you check them over for parasites, etc? Are the chickens getting into sheep droppings? Do you have one area where you store these? It's warmer now - so maybe there are fly maggots there that they're getting into? Did you check their weight? Did you mention your worming schedule?
You either have a worm issue or something bacterial going through your flocks most likely. It needs to be handled immediately. The worming will depend on when you wormed last and the weights. However, having just lost birds and now having issues with the others, you might risk losing some. It's a darned if you do and darned if you don't situation.
If your worming is completely up to date and the birds are of good weight and the droppings aren't at all frothy when fresh, I'd definitely treat for enteritis. Also remember, your birds passing diarrhea will thus be dehydrated. You'll want to make sure they're getting plenty of water and possibly electrolytes.
Yellow droppings in a flock are a serious thing. Note, they are also a sign of typhoid/salmonella/pullorum and cholera. Are your birds from tested stock? Or this could also be something like clamydiosis, or spirochetes, or (if sulfurous) blackhead. But in any case, you know that this kills. I'm thinking colibaccillosis, or E. coli. It's a coliform bacteria, often associated with exposure to feces. Do you have well water, unchlorinated water sources, a pond that perhaps the sheep droppings are running off into, puddles from recent rains, etc?
Most cases of enteritis respond apparently to Terramycin. You can get this readily at the feedstore. While you're giving any ____mycin drug, you won't want to give any added calcium or milk products. That means your follow up with probiotics needs to wait until after the treatment is done as will use of apple cider vinegar. Also keep the terramycin in a light-preventing container (like white, etc) not a clear one. Give as directed to your poultry as the sole source of water for the number of days prescribed - not one day less or you'll get resistant bacteria and have a major problem. Then for the same number of days you treated (in your case, twice the number of days) I'd give probiotics every other day. If you treat for 7 days, give probiotics every other day for 14 days. Until you find the source of infection, you'll want to build up the guts to help them do their own fighting.
Please also note the information in Glenda's post about what helps fight E. coli. I see no harm in giving vitamin E during treatment, and then continuing it with the probiotics after treatment.
In the mean time, take a good walk around the property and try to solve the 'why'. Sometimes things can pop up that we dont' realize are happening. Also realize that you could have infection in your sheep if this goes untreated. Poop runoff carries bacteria, and it's the rainy season.
I truly hope this helps.
